The last decade has witnessed the transformation of personal communication brought about by the widespread adaptation of handheld wireless communication technology. The roadmap for future development of wireless communications points to increased bandwidth. Increased bandwidth affords the opportunity to exchange high bandwidth data such as still images and video. Recently, handheld wireless communication devices (e.g., cellular telephones) that have built-in digital cameras have been introduced. Such devices allow voice and text communications to be augmented with pictures or videos. The digital cameras may be also be used to read bar codes or for other image data input applications, further enhancing the wireless communication devices' functionality.
The optical design of miniature digital camera lenses is quite different from the design of conventional camera lenses. A common challenge in designing a digital camera lens that is to be incorporated into a handheld wireless communication device is that a relatively small space is typically allocated to accommodate the camera lens. Another challenge is that the image sensors used in digital cameras that are to be integrated into handheld wireless communication devices typically are smaller, and particularly in the case of multi-megapixel sensors, have pixels that are closer in size to the theoretical resolution limit that is imposed by diffraction effects. As the theoretical resolution is approached, the design of the lenses becomes more difficult, especially for low f-number lenses, which are desirable for good performance under low lighting conditions.
Certain miniature digital camera lenses have been proposed that include molded plastic or glass aspheric lens elements. Given the wide range of temperature variations, from −15 C to 40 C, and humidity variations that handheld wireless communication devices are typically subjected to, there is a risk of environmentally induced degradation of plastic lens elements. Additionally, maintaining manufacturing tolerances for aspheric lens elements increases the costs associated with their use.
Up to now, the number of pixels in image sensors used in cameras in handheld wireless communication devices has typically been limited to 1.3 megapixels. In a well-designed digital camera, the camera lens should be capable of imaging a scene at a resolution that, at least, approaches the pitch of pixels in the image sensor. The desire to increase the resolution of the image sensors used in cameras in handheld wireless communication devices into the multi-megapixel range, coupled with the constraint on available space, increases the challenge of designing a lens that has sufficient resolution.